Debris reducing disk clamp for disk drives

ABSTRACT

A disk clamp for clamping a plurality of disks within a disk drive has a single fastening hole located at its symmetrical center sized to pass the shaft of a screw having a head diameter larger than the fastening hole. The screw fastens the disk clamp to a motor hub supporting the plurality of disks. The disk clamp has a moat around the fastening hole, at a maximum diameter that is smaller than the head diameter of the head on the fastening screw. The moat may be circular, have spike trenches angled toward the fastening hole, or be spiral. The diameter of the spiral moat decreases in a clockwise or counterclockwise direction toward the fastening hole. The midsection of the disk which the screw head covers is biased at a negative angle toward the fastening hole forcing particles generated during assembly toward the fastening hole of the disk clamp.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to disk drives and more specifically, to adisk clamp for a disk drive that reduces debris migration onto the disksurface.

2. Description of Related Art

Work stations, personal computers and laptop computers require diskdrives that provide a large amount of data storage within a minimalphysical area. A disk drive typically includes one or more hard disksthat are rotated at a constant high speed by a spindle motor. Generally,disk drives operate by positioning a transducer or read/write head overrespective tracks on the disks. The information is written to and readfrom tracks on the disks through the use of an actuator assembly whichrotates during a seek operation. The actuator is coupled to controlelectronics which control the positioning of the actuator and theread/write functions of the transducer. A typical actuator assemblyincludes a plurality of actuator arms which extend towards the diskswith one or more flexures extending from each of the actuator arms.Mounted at the distal ends of each of the flexures is a head which actsas an air bearing enabling the head to fly in close proximity above thecorresponding surface of the associated disk. The demand for increasingdensity of information stored on these disks is becoming greater andgreater for a multitude of reasons. The increase of multi-user andmulti-tasking operating system work stations which provide an operatingenvironment requiring the transfer of large amounts of data to or fromthe hard disks, large application programs, the popularity of notebookand laptop computers and the continuing trend toward higher performancemicroprocessors all contribute to this end. The structural designs ofthese systems are also continually shrinking, requiring hard disk driveshaving high capacity storage capability while occupying a minimal amountof space within the system.

In order to accommodate these demands, there is a need for smaller harddisk drives which have increased storage capacity. To read this moredensely stored information, engineers have decreased the gap fly heightbetween the heads and the disks. Reducing the gap fly height leads toincreased contact between a head and the data portion of the disk duringoperation of the disk drive. Nevertheless, there has been an industrywide push to reduce the height at which transducers are maintained overthe disk surface without actually contacting the disk surface.

When a transducer flies over a rotating disk, the flying height tends tofluctuate slightly above and below a normal flying height because thedisk surface itself is not flat. At lower flying heights the variationin the fly height may cause the transducer to contact the disk surface.This intermittent contact, if repeated, can damage the transducer or thedisk and may cause drive failures.

In conventional disk drives, a stack of disks is provided on acylindrical hub of a spindle motor. A disk clamp is provided on top ofthe stack of disks on the hub. The clamp has a larger radius than thatof the hub so that the outer diameter of the clamp is in contact withthe top disk. A plurality of screws, or a single screw, fit throughholes located in the disk clamp. These screws (screw) are threaded intobores in the hub. When a screw is tightened, the force applied to themidsection of the disk clamp is transferred to the outer circumferenceof the disk clamp which contacts the disk surface. This force securesthe disks to the spindle motor hub. The disks must be secured underconsiderable force in order to prevent any slippage of one or more disksin the presence of mechanical shocks. Even very slight slippage of adisk within a drive could result in mechanical misalignment of thetransducer which could result in data transfer errors or failure.

The assembly of the disk clamp over the disk stack tends to generateminute particles which tend to disburse on the surface of the disksthemselves. These small particles contribute to transducer contact withthe disk surface, culminating in head crashes. The more fastening screwsutilized to secure the disk clamp to the spindle motor, the moreopportunity there is for the generation of these minute particles.

Accordingly, there is a need for a disk clamp that prevents dispersal ofparticles generated during assembly of the disk stack. The presentinvention provides a solution to this problem.

SUMMARY OF THE INVENTION

The generation of debris particles during assembly of a disk pack in adisk drive is considerably ameliorated by trapping these particles in amoat formed into the disk clamp surrounding the fastening hole. The moatis covered by the head of the screw fastening the disk clamp to themotor hub. The moat keeps the debris generated during torque-down of thescrew on the inside of the moat, between the moat and fastening hole.Various moat designs have been found to be effective. Besides a circularmoat, a spike trench moat having trenches angled toward the fasteninghole, or a spiral moat are effective in retaining debris under the headof the screw. Another preferred method of retaining debris under thehead of the fastening screw biases the area surrounding the fasteninghole (the midsection) at to a negative angle towards the fastening holeof the disk clamp. This negative angle of the midsection forcesparticles generated during assembly inward, toward the fastening hole,trapping the particles under the head of the fastening screw.

BRIEF DESCRIPTION OF THE DRAWINGS

The exact nature of this invention, as well as the objects andadvantages thereof, will become readily apparent from consideration ofthe following specification, in conjunction with the accompanyingdrawings, in which like reference numerals designate like partsthroughout the figures thereof and wherein:

FIG. 1 shows a top cut-away view of an assembly of a disk drive;

FIG. 2 shows a top cut-away view of the disk stack in a disk drive;

FIG. 3 is a cross-section of the disk clamp and drive motor hubassembly;

FIG. 4 is a perspective of a prior art disk clamp;

FIG. 5 is a top view of a disk clamp at the fastening hole, illustratingone embodiment of the invention;

FIG. 6 is a cross-section of the disk clamp at the fastening holeattached to the motor hub by a fastening screw;

FIG. 7 is a cross-section expanded view of one side of the fasteningscrew holding down the disk clamp;

FIG. 8 is a top view illustration of a disk clamp according to anotherpreferred embodiment;

FIG. 9 is a top view illustration of a disk clamp according to yetanother preferred embodiment;

FIG. 10 is a top view illustration of yet another preferred embodiment;

FIG. 11 is a cross-section of a disk clamp attached to a spindle motorhub by a single screw;

FIG. 12 is a cross-section expanded view of a disk clamp attached to amotor hub by a single screw showing an alternate preferred embodiment ofthe disk clamp; and

FIG. 13 is a cross-section expanded view of a disk clamp of FIG. 12being attached to a motor hub by a single screw showing the contact areabetween the screw head and the disk clamp.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 represents a cut-away top view of a disk drive 11 having one ormore hard disks 13 with each of the hard disks having informationwritten in a series of data tracks 16 thereon. The disk drive 11utilizes at least one transducer 15 for reading and writing informationto the hard disk 13. The transducer 15 may be a conventional conductiveelement or may be a magneto-resistive element, for example. Thetransducer 15 is connected to an actuator arm 17. The movements of theactuator arm 17 are controlled by a voice coil motor 21 to pivot about apivot junction 19. A control circuitry 23 is used to control theoperation of the actuator arm 17 and other components (not shown) withinthe disk drive 11.

During a seek operation, for example, the track position of the head 15is moved across the surface of the disk 13. The head 15 is connected tothe actuator arm 17 by a flexure 51.

The hard disk 13 may be a single disk or a stack of disks. The hard disk13 is connected to a spindle motor (not shown) by a disk clamp 25.According to the present invention, the disk clamp attaches the harddisk 13 to the hub of the spindle motor by a screw 29. A plurality ofholes 27 are located in the disk clamp 25 circumferentially spaced aboutthe fastening screw 29.

The disk clamp 25 affixes the hard disk 13 to the hub of the motor bythe force exerted by the fastening screw 29. During operation of thedisk drive 11, the hard disk 13 is rotated by the motor, and theactuator arm 17 moves the transducer 15 across the surface of the harddisk 13 transferring data between the transducer 15 and the hard disk13.

Referring to FIGS. 2, 3 and 4, a spindle motor (not shown) carries thegenerally cylindrical hub 35 which has a cylindrical bottom flange 39and a cylindrical head 37 extending upward from the flange 39. The head37 defines a centrally located fastener bore 30. The flange 39, hub 35,head 37 and fastener bore 30 are all preferably substantiallyconcentric. It should be noted, however, that the hub may have manydifferent configurations in accordance with the present invention. Forexample, the hub can include several circumferentially spaced fastenerbores rather than a single centrally located fastener bore 30. The diskpack assembly illustrated for the disk 13 includes an annular spacer 41that is seated on the hub 35 so that it extends around the head 37 andrests on the flange 39. It should be kept in mind that the presentinvention can be used without the spacer 41. Also in an embodiment wherethe disk drive includes multiple disks 13, a plurality of spacers 41 areused to separate each of the disks 13. The disk 13 is in turn seated onthe hub 35 so that it extends about the hub head 37 and rests on thespacer 41. The disk 13 has a lower data surface 33 and an upper datasurface 31.

The disk pack assembly shown in FIG. 3 includes a disk clamp 25. Diskclamp 25 is shown separately in FIG. 4. Disk clamp 25 is centrallylocated on the upper surface 31 of the disk 13. A rim 49 forms theperiphery or outer diameter of the disk clamp 25. A concentricallylocated fastening hole 45 in the disk clamp defines a centrally locatedspace for insertion of a fastening screw 29.

It should be kept in mind that multiple circumferentially spacedfastener holes 45 may be utilized to match up with multiple fastenerbores 30 in the hub head 37. The disk clamp 25 is preferably made ofstainless steel, although it could be made of aluminum or materials oralloys having similar desired characteristics.

Fastening screw 29 extends through the fastener hole 45 of the diskclamp 25 and into the fastener bore 30 in the hub 35. The fasteningscrew 29 engages the hub 35 and draws the central midsection 43 of thedisk clamp 25 downward beyond its normal resting position, therebycreating stress and a constant downward pressure at the rim 49. The rim49 in turn applies a downward pressure on the upper surface 31 of disk13, thereby holding the disk 13 securely in place on the hub 35.

FIG. 4 illustrates a prior art disk clamp 25. A fastening hole 45 iscentrally located within the disk clamp 25 which is preferably formed asa circular member. A plurality of through holes 27 are circumferentiallylocated about the centrally located fastening hole 45 in the mainportion of the disk clamp 25. A midsection 43 surrounds the fasteninghole 45 inside the balance holes 27. Tooling holes 51, 53 are located inthe body of the disk clamp between the midsection and outer diameter ofthe disk clamp. These holes may be utilized by a spanner type tool thatis inserted during assembly to keep the disk clamp and spindle motorfrom turning as the screw attaching the disk clamp 25 is tightened.These holes are also utilized as a reference marker for locating areference for placing weights in the weight holes 27, to balance thedisk pack after assembly.

FIG. 5 is a top view of a disk clamp according to a preferred embodimentof the present invention. FIG. 5 shows the midsection area of the diskclamp 25. Surrounding the fastening hole 45 is a moat 55 that may beetched, laser cut, or metal worked (coined) into the disk clamp.

FIG. 6 is a cross-sectional view of the disk clamp 25 of FIG. 5 beingheld to the head 37 of the hub 39 (not shown). The fastening screw 29has an internal fastening slot 57 which may be hexagonal, for example.The head on screw 29 overlaps the edges of the disk clamp 25 at thefastening hole 45. Circumferentially located around the fastening hole45 is the moat 55. The moat 55 is located underneath the head offastening screw 29 when the disk clamp is being held down by the screw29.

FIG. 7 illustrates more clearly the moat 55 located under the head offastening screw 29 when the screw 29 is threaded into the hub 37.

The moat 55 has a width measured at its mouth and a depth measured fromthe surface of disk clamp 25 to the deepest part of the moat. The moatpreferably ranges in depth from 0.00068 inches to 0.00184 inches. Themoat preferably varies in width from 0.00200 inches to 0.00427 inches.

The size of the moat must not be so large that it structurally impairsthe disk clamp at this fastening point. Yet, the moat should be largeenough to perform its function of maintaining debris formed as a resultof tightening the screw 29 down over the surface of the disk clamp 25 inthe area of the fastening hole 45 between the fastening hole and themoat trapped under the head of the bolt 29.

Considerable experimentation by the inventors with the disk clamputilizing the moat as described above, surprisingly revealed that debriswithin the disk drive on the surface of the hard disks was reduced whiledebris between the moat 35 and the edge of the disk clamp hole 45 wasincreased.

FIGS. 8 and 9 illustrate alternative embodiments of the moat describedabove. Rather than a continuous moat circumferentially surrounding afastening hole, a plurality of trenches 65, 75 angled towards the centerof the fastening hole surround the fastening hole 45. Each of thetrenches 65 are angled towards the center of the fastening hole so thatparticles that are being generated by tightening of the screw onto thedisk clamp 60 are moved inward and fall into one of the multiple moats65. The angle at which the trenches 65, 75 are placed may vary. Thetrenches may be curved in a clockwise direction or counterclockwisedirection, depending on the threading direction of the screw so that thetightening of the screw is in a direction that moves particles beinggenerated into the trenches 65, 75.

FIG. 9 shows a disk clamp 71 wherein the trenches 75 have smooth tops73. These smooth tops eliminate scraping on the bottom of the screwhead, thereby reducing the number of particles generated. The number oftrenches 65, 75 used in the embodiments shown in FIGS. 8 and 9preferably vary between 4 to 12, depending on the material used for thedisk clamp and the tightening force required. The depth and width of thetrenches 65, 75 of FIGS. 8 and 9 are comparable in size to thecircumferential trench 55 shown in FIGS. 5 and 6.

Referring now to FIG. 10, a disk clamp 79 is shown having a fasteninghole 81 with a spiral moat 83 surrounding the fastening hole 81. Thespiral moat does not have a constant radial distance from center, asdoes the circumferential moat of FIG. 5. Rather, it decreases to thecenter, in a clockwise or counterclockwise direction, depending on thedirection the fastening screw threads to tighten down the disk clamp.

The diameter of the outermost portion of the spiral moat, the spiketrenches, and the circumferential moat, described above, is always lessthan the head diameter of the fastening screw.

FIGS. 11, 12 and 13 illustrate an alternate embodiment of the presentinvention which is also designed to maintain particles generated duringassembly trapped under the head of the fastening screw 29. As shown inFIG. 11, a disk clamp 25 having a fastening hole 45 within which islocated a fastening screw 29 that threads into the hub 35 by way of afastener bore 30 in hub 35. The disk clamp 25 has a midsection 87surrounding the fastening hole 45.

Standard practice in the prior art is to bias this midsection 87 so thatwhen the head of the fastening screw 29 compresses the midsection 87 ofthe disk clamp to the hub 35, the midsection 87 will flatten.

Offset angles are also used in other parts of a disk clamp. As taught inU.S. Pat. No. 7,209,320, the outside diameter of the disk clamp, at thedisk to hub contact area has an offset angle that slopes downward froman inside to outside of the disk clamp contact point. The application ofpressure during clamping will thus provide a more flat uniform contactarea along the clamp surface. The prior art does not contemplate biasingthe midsection of the disk clamp as proposed by the present invention oreven recognize the reasons for doing so.

Contrary to this general wisdom, the present invention biases themidsection 87 around fastening hole 45 of the disk clamp 25 in anegative downward direction between 0 and −3.5 degrees. This negativeangle is more clearly shown in FIGS. 12 and 13. The midsection 87 of theclamping disk 25 is angled downward when it is fastened by the head ofthe fastening screw 29. By biasing the midsection downward in thismanner, the particles generated during threading of the screw 29 intothe hub 35 are forced inward, towards the fastening hole 45. Theinventors believe that the negative angle contributes to this movementof particles. Initial contact between the head of fastening screw 29 andthe midsection 87 of the disk clamp is at the outside diameter of thescrew head, cutting off any movement of particles past this initialcontact point.

Experimentation by the inventors has found that considerably moreparticles are trapped under the head of the fastening screw 29 when themidsection 87 of the disk clamp is biased at a negative angle than ascompared to a disk clamp that is biased positively in an upwarddirection, or a disk clamp that is flat.

It should be understood that the foregoing disclosure describes only thepreferred embodiments of the invention. Various modifications may bemade therein without departing from the spirit and scope of theinvention as set forth in the claims to provide a disk clamp that trapsdebris particles generated during assembly of the disk pack in a diskdrive. The particles are trapped underneath the head of the fasteningscrew.

What is claimed is:
 1. A disk clamp for a disk drive, the disk drive including at least one storage disk supported on a hub rotated by a motor, the disk clamp comprising: a circular member having a center, a top surface and a bottom surface and an outer diameter, at least one fastening hole centrally located in the circular member sized for passing a shaft of a fastening screw that threads into the hub, the fastening screw having a head diameter larger than the shaft diameter, a moat formed into the circular member around the fastening hole, the moat having a diameter larger than the fastening hole but smaller than the head diameter of the fastening screw.
 2. The disk clamp of claim 1 wherein the depth of the moat surrounding the fastening hole is about 0.00068 inches to 0.00184 inches.
 3. The disk clamp of claim 1 wherein the width of the moat surrounding the fastening hole is about 0.00200 inches to 0.00427 inches.
 4. The disk clamp of claim 1 wherein the diameter of the moat surrounding the fastening hole places the moat closer to the fastening hole than the head diameter of the fastening screw.
 5. The disk clamp of claim 1 wherein the moat comprises a plurality of spike trenches surrounding the fastening hole, each trench angled toward the center of the fastening hole.
 6. The disk clamp of claim 5 wherein the spiked trenches are straight.
 7. The disk clamp of claim 5 wherein the spiked trenches are curved in a clockwise or counterclockwise direction, depending on the thread direction of the fastening screw.
 8. The disk clamp of claim 5 wherein the top of the trenches are smooth.
 9. The disk clamp of claim 5 wherein the spiked trenches are about 0.00068 inches to 0.00184 inches in depth.
 10. The disk clamp of claim 5 wherein the spiked trenches are about 0.00200 inches to 0.00427 inches wide.
 11. The disk clamp of claim 5 wherein 4 to 12 spike trenches surround the fastening hole.
 12. The disk clamp of claim 1 wherein the moat spirals with a decreasing diameter toward the center of the fastening hole in a clockwise or counterclockwise direction, depending on the thread direction of the fastening screw.
 13. The disk clamp of claim 12 wherein the outside diameter of the moat is smaller than the head diameter of the fastening screw.
 14. The disk clamp of claim 13 wherein the spiral moat has a depth of about 0.00068 inches to 0.00184 inches.
 15. The disk clamp of claim 12 wherein the spiral moat has a width of about 0.0020 inches to 0.0047 inches.
 16. a disk clamp for a disk drive, the disk drive including at least one storage disk supported on a hub rotated by a motor, the disk clamp comprising: a circular member having a center, a top surface and a bottom surface and an outer diameter, at least one fastening hole centrally located in the circular member, a midsection surrounding the fastening hole, the midsection being biased at a downward angle toward the fastening hole.
 17. The disk clamp of claim 16 wherein the downward angle of the midsection is between 0° and −3.5°.
 18. The disk clamp of claim 16 wherein the fastening hole is sized for passing a shaft of a fastening screw that threads into the hub, the fastening screw having a head diameter larger than the shaft diameter.
 19. The disk clamp of claim 18 wherein the midsection surrounding the fastening hole has a diameter equal to or less than the head diameter.
 20. The disk clamp of claim 17 wherein the downward angle of the midsection is between 0° and −3.5°. 